The present invention relates to novel N-acetylmannosamine dehydrogenase (hereinafter referred to as N-AMDH) which acts upon N-acetylmannosamine (hereinafter referred to as N-AM) to convert it into N-acetylmannosaminolactone and, at the same time, reduces nicotinamide adenine dinucleotide (NAD) into reduced nicotinamide adenine dinucleotide (NADH), as well as to a process for producing N-AMDH, an enzymatic method for quantitatively analyzing N-AM or sialic acid (hereinafter referred to as SA), and a kit for the quantitative analysis. 2. Description of the Prior Art
In the current clinical tests, SA in serum is measured, and this plays an important role in the diagnoses of acute and chronic inflammations, shocks, trauma, myocardial infarction, diabetes mellitus, liver diseases, cancers, etc.
The measurements of SA are roughly classified into chemical method and enzymatic method.
The chemical method is being gradually replaced by the enzymatic method of higher accuracy, because chemical method is inferior in various points such as specificity, workability, dangerousness of the agents used in its, etc.
Until today, method A and method B have been proposed as the enzymatic method, according to a rough classification.
Methods A and B are identical in that neuraminic acid aldolase is reacted upon SA to decompose the latter into N-AM and pyruvic acid. However, they are different from each other in that according to method A, N-AM is treated with acylglucosamine-2-epimerase and N-acetylhexosamine oxidase to form hydrogen peroxide and the latter is analyzed, while according to method B, pyruvic acid is treated with pyruvic acid oxidase or lactic acid dehydrogenase (LDH) to form hydrogen peroxide or NADH, respectively, and they are analyzed.
Method A is disadvantageous in that the existence of acylglucosamine-2-epimerase complicates the system, and method B is disadvantageous in that it is influenced by the endogenous pyruvic acid.